356 research outputs found
Dissociation and ionization of small molecules steered by external noise
We show that ionization and dissociation can be influenced separately in a
molecule with appropriate external noise. Specifically we investigate the
hydrogen molecular ion under a stochastic force quantum mechanically beyond the
Born-Oppenheimer approximation. We find that up to 30% of dissociation without
ionization can be achieved by suitably tuning the forcing parameters.Comment: 13 pages, 6 figure
Dissociation spectrum of H from a short, intense infrared laser pulse: vibration structure and focal volume effects
The dissociation spectrum of the hydrogen molecular ion by short intense
pulses of infrared light is calculated. The time-dependent Schr\"odinger
equation is discretized and integrated in position and momentum space. For
few-cycle pulses one can resolve vibrational structure that commonly arises in
the experimental preparation of the molecular ion from the neutral molecule. We
calculate the corresponding energy spectrum and analyze the dependence on the
pulse time-delay, pulse length, and intensity of the laser for nm. We conclude that the proton spectrum is a both a sensitive probe of the
vibrational dynamics and the laser pulse. Finally we compare our results with
recent measurements of the proton spectrum for 55 fs pulses using a Ti:Sapphire
laser (nm). Integrating over the laser focal volume, for the
intensity W cm, we find our results are in
excellent agreement with these experiments.Comment: 17 pages, 8 figures, preprin
Enhanced ionization in small rare gas clusters
A detailed theoretical investigation of rare gas atom clusters under intense
short laser pulses reveals that the mechanism of energy absorption is akin to
{\it enhanced ionization} first discovered for diatomic molecules. The
phenomenon is robust under changes of the atomic element (neon, argon, krypton,
xenon), the number of atoms in the cluster (16 to 30 atoms have been studied)
and the fluency of the laser pulse. In contrast to molecules it does not
dissappear for circular polarization. We develop an analytical model relating
the pulse length for maximum ionization to characteristic parameters of the
cluster
Nuclear classical dynamics of H in intense laser field
In the first part of this paper, the different distinguishable pathways and
regions of the single and sequential double ionization are determined and
discussed. It is shown that there are two distinguishable pathways for the
single ionization and four distinct pathways for the sequential double
ionization. It is also shown that there are two and three different regions of
space which are related to the single and double ionization respectively. In
the second part of the paper, the time dependent Schr\"{o}dinger and Newton
equations are solved simultaneously for the electrons and the nuclei of H
respectively. The electrons and nuclei dynamics are separated on the base of
the adiabatic approximation. The soft-core potential is used to model the
electrostatic interaction between the electrons and the nuclei. A variety of
wavelengths (390 nm, 532 nm and 780 nm) and intensities (
and ) of the ultrashort intense laser
pulses with a sinus second order envelope function are used. The behaviour of
the time dependent classical nuclear dynamics in the absence and present of the
laser field are investigated and compared. In the absence of the laser field,
there are three distinct sections for the nuclear dynamics on the electronic
ground state energy curve. The bond hardening phenomenon does not appear in
this classical nuclear dynamics simulation.Comment: 16 pages, 7 figure
How to observe the Efimov effect
We propose to observe the Efimov effect experimentally by applying an
external electric field on atomic three-body systems. We first derive the
lowest order effective two-body interaction for two spin zero atoms in the
field. Then we solve the three-body problem and search for the extreme
spatially extended Efimov states. We use helium trimers as an illustrative
numerical example and estimate the necessary field strength to be less than 2.7
V/angstrom.Comment: 4 pages, 2 postscript figures, psfig.sty, revte
Adherence to a Treat-to-Target Strategy in Early Rheumatoid Arthritis: Results of the DREAM Remission Induction Cohort
Introduction\ud
Clinical trials have demonstrated that treatment-to-target (T2T) is effective in achieving remission in early rheumatoid arthritis (RA). However, the concept of T2T has not been fully implemented yet and the question is whether a T2T strategy is feasible in daily clinical practice. The objective of the study was to evaluate the adherence to a T2T strategy aiming at remission (Disease Activity Score in 28 joints (DAS28) < 2.6) in early RA in daily practice. The recommendations regarding T2T included regular assessment of the DAS28 and advice regarding DAS28-driven treatment adjustments. \ud
\ud
Methods\ud
A medical chart review was performed among a random sample of 100 RA patients of the DREAM remission induction cohort. At all scheduled visits, it was determined whether the clinical decisions were compliant to the T2T recommendations. \ud
\ud
Results\ud
The 100 patients contributed to a total of 1,115 visits. The DAS28 was available in 97.9% (1,092/1,115) of the visits, of which the DAS28 was assessed at a frequency of at least every three months in 88.3% (964/1,092). Adherence to the treatment advice was observed in 69.3% (757/1,092) of the visits. In case of non-adherence when remission was present (19.5%, 108/553), most frequently medication was tapered off or discontinued when it should have been continued (7.2%, 40/553) or treatment was continued when it should have been tapered off or discontinued (6.2%, 34/553). In case of non-adherence when remission was absent (42.1%, 227/539), most frequently medication was not intensified when an intensification step should have been taken (34.9%, 188/539). The main reason for non-adherence was discordance between disease activity status according to the rheumatologist and DAS28. \ud
\ud
Conclusions\ud
The recommendations regarding T2T were successfully implemented and high adherence was observed. This demonstrates that a T2T strategy is feasible in RA in daily clinical practic
Exact field ionization rates in the barrier suppression-regime from numerical TDSE calculations
Numerically determined ionization rates for the field ionization of atomic
hydrogen in strong and short laser pulses are presented. The laser pulse
intensity reaches the so-called "barrier suppression ionization" regime where
field ionization occurs within a few half laser cycles. Comparison of our
numerical results with analytical theories frequently used shows poor
agreement. An empirical formula for the "barrier suppression ionization"-rate
is presented. This rate reproduces very well the course of the numerically
determined ground state populations for laser pulses with different length,
shape, amplitude, and frequency.
Number(s): 32.80.RmComment: Enlarged and newly revised version, 22 pages (REVTeX) + 8 figures in
ps-format, submitted for publication to Physical Review A, WWW:
http://www.physik.tu-darmstadt.de/tqe
Strong field double ionization of H2 : Insights from nonlinear dynamics
The uncorrelated (``sequential'') and correlated (``nonsequential'') double
ionization of the H2 molecule in strong laser pulses is investigated using the
tools of nonlinear dynamics. We focus on the phase-space dynamics of this
system, specifically by finding the dynamical structures that regulate these
ionization processes. The emerging picture complements the recollision scenario
by clarifying the distinct roles played by the recolliding and core electrons.
Our analysis leads to verifiable predictions of the intensities where
qualitative changes in ionization occur. We also show how these findings depend
on the internuclear distance
Adherence to a treat-to-target strategy in early rheumatoid arthritis:results of the DREAM remission induction cohort
INTRODUCTION: Clinical trials have demonstrated that treatment-to-target (T2T) is effective in achieving remission in early rheumatoid arthritis (RA). However, the concept of T2T has not been fully implemented yet and the question is whether a T2T strategy is feasible in daily clinical practice. The objective of the study was to evaluate the adherence to a T2T strategy aiming at remission (Disease Activity Score in 28 joints (DAS28) < 2.6) in early RA in daily practice. The recommendations regarding T2T included regular assessment of the DAS28 and advice regarding DAS28-driven treatment adjustments. METHODS: A medical chart review was performed among a random sample of 100 RA patients of the DREAM remission induction cohort. At all scheduled visits, it was determined whether the clinical decisions were compliant to the T2T recommendations. RESULTS: The 100 patients contributed to a total of 1,115 visits. The DAS28 was available in 97.9% (1,092/1,115) of the visits, of which the DAS28 was assessed at a frequency of at least every three months in 88.3% (964/1,092). Adherence to the treatment advice was observed in 69.3% (757/1,092) of the visits. In case of non-adherence when remission was present (19.5%, 108/553), most frequently medication was tapered off or discontinued when it should have been continued (7.2%, 40/553) or treatment was continued when it should have been tapered off or discontinued (6.2%, 34/553). In case of non-adherence when remission was absent (42.1%, 227/539), most frequently medication was not intensified when an intensification step should have been taken (34.9%, 188/539). The main reason for non-adherence was discordance between disease activity status according to the rheumatologist and DAS28. CONCLUSIONS: The recommendations regarding T2T were successfully implemented and high adherence was observed. This demonstrates that a T2T strategy is feasible in RA in daily clinical practice
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